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 Post subject: Zenith Trans Oceanic L600
PostPosted: Jun Fri 07, 2019 9:44 pm 
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Joined: Jun Fri 07, 2019 9:17 pm
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Location: Winter Park, FL
I was given this radio. It briefly worked and then started giving a motor boating sound from the speaker. I suspect one of the capacitors in C1 are bad.
I downloaded a poor copy of Sams Photo-fact for this radio, but it is impossible for this 84 old man to read.
If I can get the radio to work, I will also repair the power cord reel.
I would appreciate any help I could get!
David
KD4KO


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Fri 07, 2019 11:09 pm 
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Joined: Jan Tue 31, 2012 1:55 am
Posts: 8802
Location: Mountains of Mourne. Ireland.
Hello David.

Sams Photofact Set-254 Folder-13, thanks to Bill J.
viewtopic.php?p=2872995#p2872995

Nostalgia air - Transoceanic resource library.
This archived page June 8 2012 works for all downloads.
https://web.archive.org/web/20120608163404/http://www.transoceanic.nostalgiaair.org/

Padgett Peterson's archived web-pages.
http://antiqueradios.com/forums/viewtop ... 2#p2872572


Welcome aboard... :)
73 de Greg.


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Sat 08, 2019 12:05 am 
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Location: Mountains of Mourne. Ireland.
Zenith multi-section capacitor. 22-1741
Image

Image
Large imagehttps://a4.pbase.com/o12/56/215056/1/16 ... titled.png

As I'm sure you already know...
Replace it with individual caps. Lol

Greg.


Posting photos to a forum thread...
The skinny: viewtopic.php?p=3032571#p3032571


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Sat 08, 2019 11:36 am 
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Joined: Jul Mon 26, 2010 8:30 pm
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Location: Annapolis, MD
The 3 rated at 150 volts should be replaced by parts rated 160 volts minimum---250 is better, and might not cost any more.
Also any paper/wax capacitors should be replaced.

Some say that the Selenium rectifier should also be replaced (with a Si diode), but that can wait.

_________________
-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Sat 08, 2019 1:34 pm 
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Joined: Jan Mon 16, 2012 4:15 pm
Posts: 5523
Location: Near Brandon, Iowa
Note that the "upside down christmas tree" schematic symbol indicates the B- bus in this radio, NOT metal chassis ground. (Chassis ground is indicated by the "rake" symbol.) The easiest way to find the B- bus is to locate the original multicap (tubular part mounted on top rear of chassis, with a black cardboard sleeve over it). The B- bus connects to the aluminum outer can solder lug of the multicap (and runs to various other points in the chassis- easy to see where it goes, once you locate a known "starting point" for tracing it).


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Sat 08, 2019 8:38 pm 
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Joined: Jun Fri 07, 2019 9:17 pm
Posts: 24
Location: Winter Park, FL
In line capacity of C1 A B C are correct, I isolated C1 D and it is 100MFD.
I hate give up on this repair because my arthritic back pain is too severe after a few minutes of leaning over the work.
I hate to give up (it's not in my nature)

On another subject; does anyone remember the radio mentioned below?
In 1954, an Air Force buddy, sold me a very small Zenith radio that could
fit in my pocket.
It had miniature tubes with wire leads instead of pins. I remember walking
in downtown Milwaukee with the radio in my pocket and hearing everyone
trying to locate the source of the music.
I took it with me via a Troop Ship to england, and gave it my future wife's family.
David
KD4KO


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Sun 09, 2019 3:02 pm 
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Location: Winter Park, FL
I'm still trying to detect the source of the loud 5 per second thumping sound from the speaker.


Attachments:
File comment: Audo path highlighted in yellow
Scan 1.jpg
Scan 1.jpg [ 413.62 KiB | Viewed 634 times ]
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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Sun 09, 2019 3:14 pm 
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Location: Annapolis, MD
Motor-boarding.

The low-frequency "putt--putt--putt" sound is associated with the AVC circuit, which has a time constant of roughly a tenth of a second. The root cause is any oscillation that affects the AVC voltage---most often something in the IF stages.
The first thing to check is tube shields and ground connections.

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-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Sun 09, 2019 7:42 pm 
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Location: Winter Park, FL
The schematic from https://web.archive.org/web/20120608163 ... iaair.org/ is very clear, but it is not correct for what I'm trying to service.
The one from https://app.box.com/s/0uzphpfmcpqmr4q0b7macnbqx58jbu7a is correct but hard to read.

David
KD4KO


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Mon 10, 2019 4:19 pm 
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Joined: May Sat 06, 2006 4:03 am
Posts: 3375
Location: ZIP 23831 South of Richmond, VA 25 miles down the pike.
Your reader does not give you a zoom capability?

Bill J.


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Mon 10, 2019 7:51 pm 
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Joined: Jun Fri 07, 2019 9:17 pm
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Location: Winter Park, FL
I can zoom until it fills my 27 inch screen, but it will not allow me to scroll around.
I printed the PDF of the Sams Photofact, but have to get some Scotch Tape to join the sections together.
I was told that the pulsing sound emitting from the speaker was caused my the AVC.
I am not familiar enough about the AVC circuit of this 1954 radio.
I wonder if someone would trace the AVC path for me?

https://app.box.com/s/0uzphpfmcpqmr4q0b7macnbqx58jbu7a


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Tue 11, 2019 2:37 am 
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The AGC is not directly causing the "pulsing sound"--AKA motorboating. The cause is something oscillating--most lightly the IF stages.

The AGC circuit sets up a relaxation oscillator. The oscillation causes a large AGC signal, which shuts down one or more tubes. This in turn causes the oscillation to stop---then the AGC voltage drops, the tube(s) come back on, and the cycle repeats.

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-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Tue 11, 2019 2:55 am 
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Here's the beginning of the AGC circuit. At the large red dot, we have the audio / AGC composite signal. On the AGC circuit, the audio is filtered out.
The 2 arrows are the beginning of the paths to various tubes. Note that the volume control is part of the DC circuit
Attachment:
ZTO_L600_AGC.jpg
ZTO_L600_AGC.jpg [ 49.61 KiB | Viewed 532 times ]

_________________
-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Tue 11, 2019 12:02 pm 
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Joined: Jun Fri 07, 2019 9:17 pm
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Location: Winter Park, FL
Thank you pixellany.
I figured that the additional secondary winding of T1 had something to do with the AGC, so I cut the green wire. The radio still sound like one cylinder engine .
When I first turned the radio on, the audio gain control was extremely noisy. I didn't have any cleaner, so I used WD-40 to clean the carbon. It has been put-putting ever since.


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Tue 11, 2019 1:31 pm 
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Joined: Jun Fri 07, 2019 9:17 pm
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Location: Winter Park, FL
pixellany,
I forgot to mention, the radio did pick up a BC station through the crackling of the volume control.


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Tue 11, 2019 1:34 pm 
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Joined: Dec Tue 23, 2014 6:51 pm
Posts: 1248
Location: N. Palm Bch, Fl.
I had the same type of problem with an A600 last year. Do a search here for "The Chassis from Hell" rather than me trying to explain it again. I never would have found the problem without a scope. I created a problem years ago using WD40 and now that can stays in the shed where it belongs.

Good luck with your problem.
Freeman


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Tue 11, 2019 2:24 pm 
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KD4KO wrote:
Thank you pixellany.
I figured that the additional secondary winding of T1 had something to do with the AGC, so I cut the green wire. The radio still sound like one cylinder engine .
When I first turned the radio on, the audio gain control was extremely noisy. I didn't have any cleaner, so I used WD-40 to clean the carbon. It has been put-putting ever since.


That connection to T1 is audio feedback, and not directly associated with the AGC**. I would not expect the set to work correctly without it. Don't attempt to diagnose the problem with it disconnected.

Check the volume control with an ohmmeter---one lead to either end, and the other lead to the wiper. You should get a smooth variation in resistance as the control is turned.

WD-40 is a widely-used method of cleaning controls. While some controls do not recover, I have NEVER had one be damaged by WD-40.




**There is a potential interaction in that the AGC is taken at the top of the volume control. However, I'm not sure that oscilation in the AF stages gives the same result on the AGC line as does oscillation in IF stages.

_________________
-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Tue 11, 2019 2:55 pm 
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Location: Winter Park, FL
Freeman,
I no longer have a scope.
AC ripple from B- to chassis is .063 volt.

pixellany,
The total resistance of the volume control is1 meg when isolated. The WD-40 cured most of its rotation noise.


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Wed 12, 2019 1:13 am 
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this is the test we need on the volume control:
Quote:
one lead to either end, and the other lead to the wiper. You should get a smooth variation in resistance as the control is turned.

_________________
-Mark
"Measure voltage, but THINK current." --anon.


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 Post subject: Re: Zenith Trans Oceanic L600
PostPosted: Jun Wed 12, 2019 4:20 pm 
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Joined: Jun Fri 07, 2019 9:17 pm
Posts: 24
Location: Winter Park, FL
pixellany,

The volume Poi is good!
I cut the plate wire of the converter tube and applied power; still get moter boating sound.
I did the same to the plate of the IF AMP; still get motor boating sound.


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